Balloon angioplasty procedures have been used in recent years with increasing success in the treatment of obstructed arteries, such as the coronary arteries. The procedure involves advancing a catheter, having a special balloon at its distal end, to the location of the stenosis. The balloon portion of the catheter is inserted, in its deflated condition, into the stenosis and then is inflated with a liquid under high pressure to compress radially and outwardly the biological material, such as plaque, which forms the stenosis. One type of such dilatation catheter is referred to as a "fixed wire" catheter. Fixed wire catheters are characterized in that the balloon portion at the distal end of the catheter is supported on a central wire that extends through the balloon and to which at least the distal end of the balloon is attached. By way of example, U.S. Pat. Nos. 4,917,088 and 4,582,181 disclose two types of fixed wire catheters. In general, the fixed wire catheters exhibit a low profile, that is, the balloon portion can be deflated and wrapped closely about the supporting wire and, in that configuration, the catheter can be advanced to and into very narrow stenoses and into very small blood vessels. Typically, such fixed wire catheters are steerable in that they can be manipulated from their proximal end to rotate and advance the catheter. By providing the distal end of the wire, which protrudes distally of the balloon, with a slight bend, and by a combination of rotating and advancing movements, the fixed wire catheters can be advanced and steered through a patient's blood vessels to the intended location to be treated.
Although such fixed wire catheters have achieved wide spread use among physicians practising angioplasty, occasionally, they may present some difficulties. In particular, among the difficulties encountered with such fixed wire catheters is that when the core wire is rotated, that sometimes causes the balloon to twist, in an hourglass configuration, about the core wire. Such twisting can obstruct flow of inflation liquid to or from the balloon. Although flow of inflation liquid to the balloon impairs the ability of the balloon to be inflated in order to perform the angioplasty, a more serious condition is presented when the twist in the balloon prevents the balloon from being deflated. It is essentially to be able to deflate the balloon so as to periodically permit some blood flow in the artery and also to be able to withdraw the catheter after the angioplasty procedure has been completed. The consequences of inability to deflate the balloon can be very serious.
It is among the primary objects of the present invention to provide a fixed wire catheter construction in which the risk of the balloon becoming twisted in a manner that adversely effects inflation or deflation of the balloon is avoided.